Hitherto, fossil resources such as petroleum, coal, etc., have been used in large quantities but there is a limitation about the reserves thereof and hence the future of the reserves is a matter of anxiety. On the other hand, wood is a reproducible resource and has been utilized in various fields. However, the effective utilization of unused woods such as twigy woods, periodically thinned woods, etc., has not yet been practiced well and the development of more effective utilization processes of wood meal, chips, etc., by-produced as the industrial wastes in the industries utilizing woods has been desired.
As one of conventional processes for utilizing the aforesaid materials, there is a well-known technique wherein a wood meal is mixed with plastics such as a thermoplastic resin, a thermosetting resin, etc., for use as a filler or an extender. In this case thermoplastic resins are more generally used as the plastic. However, since in such a utilization process a wood meal is physically mixed with the foregoing resin, whereby the wood meal exists in the resin in the state of simple dispersion, as well as a wood meal is generally low in specific gravity and is bulky, it is very difficult to uniformly and finely disperse the wood meal in a resin Also, since wood is a material having a poor thermoplasticity and is not fused by heating the moldings obtained-by mixing the wood meal with a thermoplastic resin show the appearance of the form of the wood meal itself and also show the reduction in smoothness and luster of the surface itself. Furthermore, the dimensional stability of the moldings is reduced by water absorption as well as the strength and hardness of the moldings are also reduced by water absorption.
The foregoing faults are caused in the case of using thermoplastic resins but thermosetting resins are also used for the foregoing purpose. Examples of the thermosetting resin are mainly a phenol resin, a melamine resin, a urea resin, etc. However, the use of such resins are also accompanied by the foregoing faults
On the other hand, moldings obtained by using an epoxy resin have recently been used as materials for various industrial parts due to the excellent electric property, chemical resistance, toughness, and dimensional stability. An epoxy resin has many features or merits which are not obtained by a phenol resin and a melamine resin. However, in the production of epoxy resin moldings, wood meal, chips, etc., have little been used as fillers, extenders, etc. The reason is considered to be that wood has an affinity to a resin having a high hydrophilic property in the stage of the initial condensation product, such as a phenol resin and a melamine resin but an epoxy resin is lacking in such an affinity. However, it can be said to be a very significant matter to perform the investigation of the production of woody moldings having a high additional value by forming composite materials of wood using an epoxy resin having such various features.
Also, a chemical treatment for cellulose has been practiced for a considerably long time but a chemical treatment for wood has not yet been practically developed. The reason is considered to be that wood shows a very low chemical reactivity. For example, if a wood meal is mixed with an epoxy compound with stirring under heating for binding the hydroxy group of the wood to the epoxy group of the epoxy compound by the reaction of them, but in this case the ratio of binding of the epoxy compound to the wood is very low. The reason is that wood greatly differs from the foregoing cellulose in composition and structure. That is wood is mainly composed of highly crystalline cellulose having a crystallinity of about 60 to 70%, super macro-molecular lignin having a three-dimensional network structure, and noncrystal hemicellulose. These materials exist in the cell walls of the wood in such a state that the cellulose pass among the networks of the lignin assembly, which is in a steric sponge form, in the form of a fibrillar bundle and the hemicellulose is filled in these gaps. Therefore, it is considered that the chemical reaction occuring in cellulose is very reluctant to occur in wood.
The inventors tried to produce a woody molding mainly composed of wood components by simultaneously adding a polybasic acid anhydride and a compound having two or more epoxy groups in the molecule to wood meal and then heat and press molding the mixture. However, in this case there were difficulties that not all of the epoxy groups of the epoxy compound were used for a direct bonding reaction with the wood meal and a part of the polybasic acid anhydride added at performing the heat and press molding sublimed to cause a loss of the material as well as to cause an undesirable trouble in environmental sanitation.